First contact your local office of the Clemson USDA Cooperative Extension Service and the can help identify that and can also help you get a good, reliable soil test which might do as much to control this as anything else. Many "weeds" grow in soils that are not good soils for turf grass and turf grass most often needs a good, healthy soil or it will not grow well. At the same time dig in with these simple soil tests,

1. Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
to learn more about the soil you have and what yo need to do to make that soil into something that will grow a good, healthy turf.

Here is a link that might be useful: Clemson CES

The images don't quite let me make accurate identification of the grass/weed, but it looks like Bahia grass. If so, it is a very common grass, typically planted along roadsides (on purpose) because it's so tough, drough resistant, and sturdy. It will also grow just about anywhere (no matter what the conditions are) in warm climates.

Bahia is most famous for those wiry seed heads, which can really ruin the appearance of a lawn. (It's pronounced Bah-HAY-uh, just so you know.)

Take a clump of the grass to the extension office; be sure to include some crowns and blades, as well as the flower stalks. Somone will certainly be able to identify it for you. I'm very sorry to tell you that it will be very difficult to get rid of a grassy weed in a lawn.

how do i get rid of these weeds?

Oh my. Just two weeks ago, I came home, and found about 15 pop-ups of the same exact weed in one section of my backyard. having a horrible time with getting any grass to grow in this sections, since there once was a tree in the middle of the backyard with roots still buried under the ground. For over five years I have had bare spots, with the direction of the root system. A few years ago I was able to dig up some of the area and hack away at the huge roots, but now the grass just does not want to grow here.
Have never seen this weed before, now I have 15 of them popped up in sections in this area of my backyard.
zone 7

I had TruGreen come out and identify the grass. It was Bahia grass. He told me the only way to get rid of it is with RoundUp.

I was reluctant, but I did it that fall (2008). It got rid of 75% of it, but I still have small patches. The "RoundUped" areas turned to dirt and tatch almost immediately and I replanted grass the next spring. 2 years later and it looks much better. I'm considering another RoundUp treatment on the patches, just to get rid of it for good. It spreads extremely fast since it takes about 3-4 days after mowing for a seed stem to appear.

I recommend attacking this grass ASAP if you find it in your yard. Otherwise you'll be applying RoundUp to huge areas of your lawn like I had to!

Bahia is taking over the ditches and uncultivated fields in this area. I fight it constantly.

I do not know the name of it, but my feed store sells a white powder that is mixed in water and sprayed directly on the growing plant. It slowly dies, but any ripened seed can still germinate. Thus you must repeat treatment but will eventually get it.

The downside is that the powder costs $16.00 per tablespoon.
The upside is you only use a pinch between your fingers per each gallon.
It did not bother the other weeds and grasses like Roundup does.

If anyone is interested I will inquire what the brand name is.